Everything I know about antifouling!

17th April 2022 – Dunstaffnage

Compared to the complexities of varnishing, antifouling is a simple and manageable task. Nevertheless, there is plenty of scope to cock it up. So here are a few random musings which may be of some minor help to those who may be new to boat ownership and who can’t afford to issue forth the command:

“Antifoul her and put her on my berth, I’ll be sailing on Sunday”

Everything here only relates to slow moving cruising boats. Fast racing yachts and non-displacement motor boats will need a different approach.

First things first, what brand of antifouling should I use?

God knows! It is a dark and magic science but you can’t go far wrong by asking other sailors in your area what they are using. Each person you ask will probably swear by a different product but there may be some consensus. Nowadays the active ingredient seems to be copper. If the can is heavy, that’s a very good sign. I was using Seajet Shogun 033 until the Bean Counters stopped them from making the lovely green, and then they stopped making the white too, so now I use Hempels Tiger Extra and I’m stuffed if I can tell the difference. These are eroding antifoulings which gradually ablate over the season. It’s useful to know what type of antifouling is already on the boat, just in case it is a rare type not often met with which will require a barrier coat before applying a new type.

Along the waterline it is good to use a harder antifouling as this area is liable to be scrubbed. I use International Trilux and it works well. Well it used to work well until they stopped selling it. Now I am using Hempels Hard Racing stuff which goes on nicely but I need to wait to see if it actually works (2023)*. I have never stripped the waterline so there are now about 62 coats on it, great for crunching through a bit of thin ice!

  • It seemed to work fine but this year I am using Cruiser 200 which is Internationals replacement for Trilux. Let’s see if it works.

You’ll maybe need some primer too in case there are any blemishes which need touching up. If you assume that all underwater primers do what they say on the can, then how do you choose which one to buy?

I’d go for one with fast drying times. Epifanes Underwater primer needs 24 hours between coats and 5-14 days before antifouling or launching. As it needs 6 coats it will be at least 11 days before you can even apply the antifouling!

Now, good old Seajet Underwater Primer can be overcoated in 3 hours, so you could be antifouling on the third day. It also never forms a skin in the can, how weird is that! I know which primer I’d choose for patch priming under antifouling. However, I wouldn’t recommend it below other paint systems as there can be a bonding issue. See below.

At the top of the picture you can see a square patch prime using Seajet Underwater Primer overcoated with Danboline. When the masking tape was removed a lot of the Danboline paint simply tore away with it. The primer did remain firmly bonded to the substrate.

How much should I buy?

Ah, now here lies the crux of many a fouled up fouling job. So before you swear at the manufacturers when your boat is covered in beasties, here is a little story.

I used to sell floor finishes for theatres and customers would ask how much they needed to buy. It was simple enough to calculate. They told me the stage area and based on the manufacturers recommended coverage, I would flog them the goodies. It was surprising how often they would come back a week later saying “Gosh it goes a long way, we didn’t need the second 5 L can, can I return it?”. The problem was they did need it, but they simply hadn’t applied enough. The Science Boffins had worked out what was needed and they just ignored it. Two problems would occur with the floor finishes applied too sparsely. As it was spread so thinly, it dried very quickly so it didn’t have a chance to penetrate and soak into the substrate and provide a good grip. Secondly, the coating was too thin to provide a long lasting finish before wear-through would occur and the whole process will need repeating and, worse still, it will need stripping off too!

So you need to work out roughly the wetted area of your boat. If it is a normal cruising yacht, this may help.

Take the waterline length in metres and multiply it by the beam plus the draft. Thus LWLx(B+D)= the wetted area in square metres. Hempels Tiger Xtra will cover 13 square metres per litre. The approximate wetted area of a Vertue is 24.5 square metres. Therefore, as a 2.5 L can will cover 32.5 square metres, I need to buy two cans for two coats and should have just over a litre spare.

Whatever brand you choose don’t skimp on the application. You will not get away with one coat. I say again, YOU WILL NOT GET AWAY WITH ONE COAT. So don’t even think of trying to save a few bob that way. Remember this stuff erodes away, so the correct surface thickness is crucial but not only that, with one coat there will be holidays. A holiday is a pin prick hole through the paint which has been missed. I know you did a great job, but I bet you the following day you will be able to find tiny little holidays in the coating to allow nasty Mr Gribble in. The second coat will sort that out. With that spare litre, you could even add a third coat on the rudder just aft of the prop and all around the waterline, just to be sure. Make sure you leave a bit for touching up under the support pads while she is in the crane slings.

So what else should I buy while I’m at the chandlers?

It partly depends on how long you want to live, and also how much you appreciate seeing things. Yes, I’m talking about a bit of PPE. Marigold gloves and overspecs or goggles are really important. Apart from anything else, if you are wearing Marigolds and your brand new £700 iPhone rings, you can tear off the gloves and answer it without smothering the phone in antifouling. The gloves also stop lots of nasty solvents making their way into your blood stream. Don’t tear them off inside out unless you are in a hurry, but try to pull them off by the fingers. You’ll soon find out why, but they also change colour when they are inside out making them very hard to find!

If you are going to use a brush to apply the antifouling then you will need to buy some antifouling thinners. To be honest, cleaning a roller with thinners costing £13 a litre just isn’t worth the cost benefit analysis. I use just a small glug of expensive thinners on my brushes, then I swap to White Spirits and afterwards to Brush Cleaner and then Fairy Liquid. I also use a brush spinner. But I digress.

You will of course need something to apply the concoction. Whether you choose a roller or brush is dealt with in a paragragh below.

Yellow Tesa Tape – you’ll never look back!

You will need some masking tape and I need to take this opportunity to shout out about Tesa yellow tape which is simply the bees knees. Sadly your chandler probably wont sell it, so you will have to buy the blue stuff from 3M. You will need to go around the boat loads of times – top and bottom for the waterline, then the bottom to the waterline and repeat for the second coat if there is going to be a delay between applications. You can save some money by buying cheap masking tape but when you are spending hours trying to peel the the damn stuff off and then need to buy a litre of expensive residue remover you will soon wish you took note of my sage advice.

If you haven’t got a boiler suit and want to wear those jeans again, then a Tyvek paper coverall will do the job. If you like your shoes, some Tyvek overshoes may help, but I’ve never gone that far. If you are working in the open air, and obviously not dry sanding, then a face mask is optional, however if you are splashing the stuff on, it will save getting blobs landing on your lips so it may be a worthwhile addition.

Don’t overdo the PPE, you might scare the children

Even though the boatyard made a great job with the pressure washer, I bet they missed a few patches behind the slings so some abrasive scouring pads will be handy. Green General Purpose ones are ideal, give the scummy areas a good scrub but always with a hose to hand. Never ever dry sand antifouling, you might have a mask on, but those children playing on the other side of the boatyard probably haven’t.

Make yourself comfortable!

Why bust a gut doing a simple and manageable job? Get yourself a “Hop-Up”. They are ideal for sitting on, standing on, or just putting your paint pot on. Trying to antifoul while holding a half squat is great for your thigh muscles but do you really want a workout whilst trying to prepare your boat? Talking about those low down bits, how about some knee pads. Cheap thick foam ones with Velcro straps will do the trick, or go posh and have them built into your boiler suit. For the really really low down bits and underneath, you can’t beat a roll of old carpet. You can lie there in perfect comfort watching the splashes of antifouling land on your overspecs while you gradually dose off dreaming of sailing to a land where everyone is happy – like Portmeirion.

Should I brush or roll the stuff on – that is the question

Most people use a roller but I use a brush. Most people have got bigger boats and, as using a roller is faster, it can save a bit of time. As my boat only takes two hours to antifoul there is little time advantage and I just happen to prefer a brush.

My Purdy brushes that I use for antifouling

I am lucky as I can use either hand to paint, so I never get tired! I use a 4″ Purdy Wall Brush to cover the bulk of the hull. These brushes cost about £50 so they need to be cared for. Mine is about 20 years old and will see me out. Sadly, it looks like Purdy’s Bean Counters have also been at work and they no longer make that beautiful block wall brush on the left, I expect the margins weren’t good enough. Please do not buy total crap brushes from the DIY Sheds. The hairs will fall out, they hold hardly any paint and the job will take three times as long as using a proper brush from a specialist decorating supplier.

Even if you decide to brush on your antifouling you may find a 4″ Radiator Roller with a long handle is handy for painting under the keel if it is too low to the ground to wield a paint brush.

And even if you decide to roll on your antifouling you may find a slim brush handy for painting behind the rudder, unless of course you have one of those boats where the rudder dangles from a pole. You might also want some cheap rubbish brushes for applying the primer patches.

I’ve arrived at the boat – now what?

Go back to the chandlers and buy a little scraper, then open up any wounds. Look for bubbles, cracks and water stains and have a poke around. Any bare wood will need to dry out and get primed. Hopefully you will have other things to do while you are patch priming. If not, you may just need to visit the pub.

Building up the patch priming. Also showing the newly painted prop fitted with its anode nut. See the post on Propellers for information on antifouling the prop.

Once you have the first two coats of primer on, you can get on with wet scrubbing all those bits the boatyard missed with the pressure washer. While you are getting on the required coats of primer on the patches, mask up the waterline area ready to paint. It’s best to paint the waterline first because the paint is stronger and less liable to break away when you are tearing off the masking tape after applying the fouling to the bottom.

Now what’s stirring?

Look at that lovely old stick stirrer!

Now this is very very important. Those Science Boffins who have a PHD in paint chemistry would be devastated if they thought you were about to slap the stuff on after just a quick shake of the can. You do need to stir the stuff thoroughly with a stick. Well you can stir it with anything you want, but you forgot to buy the stirrer in the Chandlers, so a stick will be fine. The thing is, even though the ingredients have been carefully selected, they all have different densities so the good copper stuff may sink to the bottom and the bonding agent may float to the top. It is a common error not to spend enough time stirring. I actually mix two different coloured antifoulings in a big builders bucket so I can see when everything is mixed. That is also why the catalyst for fillers is normally red. Here’s another tale from theatreland.

We used to sell a lot of matt glazes. The matting agents sink to the bottom of the glossy stuff. We would get complaints that the product was patchy and one side of the stage dried glossy and the other side was matt. Guess why? We ended up sticking our own “Stir well” labels on the cans.

And now what should I do?

Just get on with it and get that boat in the water!

..and if you have any helpful tips please comment below. Thanks!

Top Tips coming in so far

  1. Note the batch numbers from the base of your cans and the weather conditions on the day o application. It will help to make a claim should the product fail. Thanks to Bruce
  2. Always wear googles, learnt the hard way! Thanks to Selma

4 responses to “Everything I know about antifouling!”

  1. Hi Alasdair, A few years ago Thelma and I were asked if we could take over running a wooden boat building yard, the owners were friends and were off around the world in their wooden trawler style motor sailor, so with great trepidation we agreed. I was on a very steep learning curve as my previous occupation was in communications and electronics. The yard stocked Joton paints so I requested Joton to send one of their chemical engineers to give me the 2 day course on their paint products. One of the tips that he gave me was allways record the paint batch number from the bottom of the tin of paint and to note in the workshop diary the weather conditions prevailing on the day of application
    His reason for this is that if the customer question the effectiveness of the paint Joton would provide replacement paint and it there was a known problem with the paint Joton would pay for the removal of the paint and supply a new batch. If the batch number was not known it would be difficult to claim. Joton also provided wet film thickness gauges for use to use. I must say my time at the yard was very difficult and I pleased when the arranged to lease out the yard.

    Bruce sy Tui of Opua

    1. Hi Bruce, It sounds like you ran a very professional yard. Your suggestion is an excellent one and makes a lot of sense. I shall note the batch numbers and weather in future. I can remember clients complaining to me about waterborne glazes drying cloudy but when we asked when they applied the product and linked it to historical weather data it was nearly always due to the application taking place below the recommended temperature.
      Thanks for the tip.
      Regards, Alasdair

  2. My only recommendation is to wear googles. Especially if you’re getting your 5 year old to help anitfoul. Never being one to listen to his father too closely, Jacobus loaded up his roller with the thickest layer of anti foul and merrily rolled away above his head reaching as high as he could. Looking up to watch what he was doing much of the paint splattered into his non wearing goggle eyes. A swift shout out in pain and yelling and falling on the floor ensued with his somewhat sheepish parents having to call the emergency services, more worried about social services asking us what we were doing using child labour. Needless to say now some 16 odd years later he still has both eyes and no harm done. Social services did call us but that’s another story…

    1. Five year olds are ideal for painting the bilges, under the engine and other hard to access spaces like the top of the mast but sadly Facebook refused to accept my advert for some youngsters despite offering £2.00 per hour AND googles. What is this world coming to?

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